In exploring for hydrocarbons, a variety of techniques are employed to gain a better understanding of the subterranean environment. For example, the resistivity of reservoirs below the ground surface or seafloor has been detected to facilitate exploration for hydrocarbon. In some operations, controlled source electromagnetic surveys are used to help confirm the presence of a resistive fluid, e.g. liquid or gas, within a favorable hydrocarbon trap structure which may indicate the presence of hydrocarbons. Magnetotelluric surveys also have been used to produce subsurface structural images in certain environments. However, the electromagnetic survey interpretations often fail to sufficiently account for resistive anisotropy, the difference in horizontal and vertical electrical resistivities of a subsurface volume of earth. Inversion of the surface electromagnetic survey data can yield substantial error due to the non-uniqueness of inversion models fitting the observed data with many parameters unconstrained.
In some environments, seismic surveys also can be used to measure the acoustic response of the earth and its specific structure or layering. However, acoustic information does not help discriminate between the type of liquid because the propagation difference varies little between fluids. Seismic surveys also do not enable identification of well gas saturations because acoustic propagation through small quantities or large quantities of gas is similar. Other measurements also have been used to help gain a better understanding of the subterranean structures and potential reservoirs. However, such techniques and measurements also fail to sufficiently account for anisotropy of the overburden.